The spin torque oscillator (STO) is a type of microwave device based on the sustained precession of a magnetic moment due to torque transferred from a spin polarized current. A STO has capabilities for high frequency operation (approaching 100 GHz), wide electrical and magnetic tuning range (tens of GHz), small size (down to tens of nm), and compatibility with silicon CMOS and III-V back-end processes.
These attributes make STOs useful for the variety of electrically controlled oscillator applications, such as microwave generator, signal-processing, frequency synthesis integrated circuits (ICs), millimeter-wave high-speed radio links, and cruise control radars. STOs are also useful for the wide range of applications for magnetic field sensors, including highly sensitive, nanoscale read/write heads and biosensors for immunomagnetic assays. In addition, computing with arrays of STOs has attracted much attention recently.
Previously, the application of STOs has been hindered by low output power and poor spectral purity. The previously available STO's output power is limited by its size, which is small (<100 nm) to insure that only a single magnetic domain exists within the structure, thereby providing a well-defined mode of oscillation. Phase noise is inherently high in such STOs due to nonlinearities in the dynamics and sensitivities to thermal magnetic fluctuations, as well as fluctuations in current, field and even oscillation amplitude.